Methods and systems for control of generating units with minimum steam losses



3,210,555 ATING E. S. BRISTOL TEMS F Oct. 5, 1965 METHODS AND SYS OR CONTROL OF GENER UNITS WITH MIN IMUM STEAM LOSSES 2 Sheets-Sheet 1 Filed April 12, 1963 O om am cm a Max Megawatts Megawatts E. s. BRISTOL 3,210,555 METHODS AND SYSTEMS FOR CONTROL OF GENERATING Oct. 5, 1965 UNITS WITH MINIMUM STEAM LOSSES Filed April 12, 1963 2 Sheets-Sheet 2 United States Patent 3,210,555 -METHODS AND SYSTEMS FOR CONTROL OF GENERATKNG UNITS; WITH MINIMUM STEAM LOSSES Edward S. Bristol, Philadelphia, Pa., assignor to Leeds and Northrup Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Apr. 12, 1963, Ser. No. 272,770 Claims. ((31.290-40) This invention relates to systems and methods for controlling a generating unit comprising an electrical generator, a steam turbine for driving the generator and a boiler for supplying steam to the turbine.

In such generating units, the multiple-element input valve of the turbine has a series of lower-efficiency ranges each extending from the closed position of the corresponding valve element for an appreciable fraction of its total travel range. Most commonly for controlling output generation of the unit, the steam input valve was progressively opened for increased generation and progressively closed for decreased generation, the steam pressure being maintained substantially constant by varying the inputs to the boiler: less commonly, for controlling output generation, the boiler-inputs were progressively increased and decreased for increased and decreased generation and the steam-input valve was adjusted to maintain the steam pressure constant. With either method of control, the unit operates at appreciably lower steamutilization efliciency for valve positions in the high-loss ranges.

It is an object of the present invention to provide a control band of steam pressure utilized to minimize operation of the unit with the steam valve in positions corresponding with lower efficiency of steam utilization and providing for continuous variation of generation within a generation-range.

In accordane with the present invention, steam pressure is maintained substantially constant only so long as the demand for increased or decreased generation does not require movement of the steam valve into one of its highloss ranges. When a required generation at constant steam pressure corresponds with a valve position within a high-loss range, the valve is instead positioned at one or the other of assigned limits of that range and the rate of production of steam is varied to change the steam pressure and therefore the rate of flow of steam through the temporarily fixed valve-opening.

More particularly: (a) when the steam valve is not po sitioned within one of its high-loss regions, the generation is increased by further opening the steam valve and increasing the rate of steam produced so as to meet the higher demand with steam pressure held substantially at a desired normal value. Then in accordance with the present invention (b) when further increase of generation by such procedure would require movement of the steam valve within a high-loss region, the steam valve is temporarily held fixed and only the production of steam is increased; the resulting increase of steam pressure then effects increase of steam flow to the turbine. For still further increase of generation, the preceding procedure is followed until steam pressure reaches an assigned high limit. (c) Any further increase action is applied solely to further open the steam valve. Because such further increased output is supplied from stored energy, the steam pressure is thereby shortly reduced to normal and, if the steam valve has by then been moved beyond the highloss region, procedure per (a) is resumed; otherwise procedure per (b) is repeated.

Further, ((1) when the steam valve is Within a low-loss region generation is decreased by joint further closing of 3,210,555 Patented Get. 5, 1965 the steam valve and decrease of rate of steam production so as to meet the lower demand with substantially constant steam pressure. (e) If such procedure would require the steam valve to move within a high-loss region, further decrease action is applied solely further to close the steam valve to reduce the steam flow. The closing of the valve with fixed rate of steam production results in an increased pressure which requires further closing of the valve. In consequence, the valve is moved rapidly in closing direction so as to reduce steam flow in the absence of a decrease in steam production. (f) If the preceding procedure moves the steam valve beyond the high-loss region without raising steam pressure to an assigned high limit, procedure per (d) is resumedbut if high limit steam pressure is reached, further decrease action is applied solely to rate of steam production until steam pressure is reduced to normal, when procedure per (e) is resumed.

In general, action to move the steam valve promptly through high-loss regions per (c) and (e) above is facilitated by use of an adequate band of controlled steam pressure variation. If an assigned steam pressure limit is reached before a high-loss valve region is traversed, a portion of the procedure can be modified as indicated in (c) and (f).

Further in accordance with the invention, the generating unit is provided with position-responsive means producing signals indicative of valve position, pressure-responsive means for producing signals indicative of steam pressure deviations from a set point, memory means for producing signals indicative of which assigned limit was last attained by the steam pressure, and means for producing signals indicative of demands for increase and decrease of generation. These signals, as collated by an operator or by logic circuitry, provide the information for control of the unit in accordane with the method aspects of the invention. With logic circuitry, all of the various combinations of coexistent signals are converted to output signals simply calling for opening or closing of the steam valve and increase or decrease in the rate of steam production. Such output signals may be used to inform the operator of the required execution without need by him to collate the signals of the various responsive devices, but preferably such signals are used to effect automatic execution of the operations required to effect generation changes with more eflicient steam utilization.

The invention further resides in methods and systems having features of novelty and utility hereinafter described and claimed.

For a more complete understanding of the invention, reference is made to the following description of specific embodiments and to the attached drawings in which:

FIG. 1 schematically illustrates a control system in which the collation of signal information concerning operating variables of a generating unit and the adjustment of its boiler and prime-mover input are performed by an operator;

FIGS. 2 and 3 are explanatory figures referred to in discussion of FIGS. 1 and 2; and

FIG. 4 schematically illustrates a control system in which the collation of signal information is effected by logic circuitry and the adjustments of boiler input and turbine input may be effected automatically.

Referring to FIG. 1, the generating unit 10 comprises an alternator or other electrical generator 11 for supplying current to feedline 12, a turbine or other primemover 13 for driving the generator, and a boiler 14 for supplying steam to the prime-mover. Flow of steam from the boiler to the turbine is controlled by a valve means 15 which comprises a plurality of valve elements V1-V4 sequentially actuated by a reversible actuating means exemplified by motor 16. The motor 16 may actuate the valve eitherdirectly or indirectly by changing the setting of a speed-responsive governor operating the valve means. The controller 17 for motor 16 includes the switch buttons 17U, 17D in any conventional reversing circuit and selectively operable to increase or decrease the stem-valve opening. The rate at which steam is produced by the boiler may be controlled by means for varying any one or more of the boiler inputs, such as fuel, air, water, etc. and here exemplified by fuel valve 18 and its reversible actuating motor 19. The controller 20 for motor 19 includes switch buttons 20U, 20D selectively operable to increase or decrease the setting of valve 18.

The electrical output required of the unit to meet its share of the existing demand upon the distribution system connected to the unit 10 by feedline 12 may be indicated by the instrument 2]. which generally receives such information from a load dispatchers office. The actual generation delivered by unit 10 to the feedline 12 may be indicated by a Wattmeter 22. The pressure of steam available for supply to the prime-mover 13 via valve may be indicated by meter 23.

With the system as thus far described, control of the actual electrical output of generator 11 as measured by Wattmeter 22 for matching of its required generation as exhibited by indicator 21 is, in accordance with prior practice, effected by operating the controller to maintain constancy of the steam pressure at a selected value corresponding with the set point index 23A of indicator 23 While operating the controller 17 to change the position of steam valve 15, i.e., progressively increasing the valve opening'when there is a demand for increased generation and progressively decreasing the valve opening When there is a demand for decreased generation. As now explained, this usual mode of controlling the output of unit 10 is subje ct to undesirably high throttling losses in the steam valve means 15.

Referring to FIG. 2 as exemplary of the idealized relationship between steam valve position and actual generation for constant steam pressure and other conditions, for outputs within the #4 range, all of the valves V1 to V3 of valve means 15 are fully open and change of the generation is effected by varying the opening of valve element V4: for outputs in the #3 range, valve V4 is fully closed, valves V1 and V2 are fully open and change of generation is effected by progressively varying the opening of valve element V3: for outputs in the #2 range, valves V4 and V3 are fully closed, valve V1 is fully open and change of generation is effected by progressively varying the opening of valve V2: for outputs in the #1 range, valves V4, V3 and V2 are fully closed and the Opening of valve V1 is progressively varied to change generation. It is not to be inferred from FIG. 2 that actual generation is necessarily a linear function of valve position or total valve travel.

- With any of the valves V1 to V4 in only slightly open position, throttling losses are high with consequent substantial reduction in efficiency of steam utilization. These regions of high throttling losses are indicated in FIG. 2 by the curve segments H1-H4. Since in actual practice the valve V1 is in a high-loss range only for a brief time during shutting down or starting up of unit 1.0, the throttling losses due to operation of the unit in region H1 are not of significance. The situation, however, is otherwise for operation in any of the valve-position regions H2H4, and it is a primary purpose of the present invention to provide a method of controlling the actual generation throughout the whole range of normal operation without incurring high losses incident to prolonged operation ofunit 10 with valve means 15 in any of its high-loss regions.

To that end, the system of FIG. 1 includes a valveposition indicator 24 suitably coupled to repeat the position of the steam admission valve 15. The segments Til-T4 of indicator 24 cooperate with a suitable index or pointer 24A to show when any of the corresponding valve elements Vl-V4 is in a high-loss range. The system of FIG. 1 also includes a Bourdon tube, or equivalent device, responsive to the steam pressure and suited for actuating a switch 26 which controls a latching or memory relay 27 associated with a pressure limit indicator 28 exemplified by light bulbs 28H28L.

When the steam pressure rises to preselected upper limit, for example, a few percent above the set point, the closure of switch contacts 26A, 26C completes a circuit including the coil of relay 27, the current source 29 and the current-limiting resistor 30. With the relay 27 energized, its movable contact 310 engages fixed contact 31A to complete a circuit from source 29 through the highlimit indicator 28H. The movable contact 32C of relay 27 concurrently engages fixed contact 32A to complete a hold-in or memory circuit shunting the contacts 26A, 26C of the pressure-responsive switch 26. Thus, the relay 27 remains energized despite separation of contacts 26A, 26C of the pressure switch 26 until the steam pressure falls to a preselected lower limit, for example, the set point or slightly below the set point. At that time the contacts 26B, 26C of the pressure-responsive switch are closed to provide a short circuit for the coil of relay 27. The resistor 30 limits the current drawn from source 29 While contacts 26B, 26C are in engagement. With relay 27 thus effectively deenergized, its contact 32C moves away from contact 32A to break the hold-in circuit. Contact 31C of relay 27 moves out of engagement with contact 31A to extinguish the high-limit bulb 28H and into engagement with contact 31B to excite the low-limit bulb 28L. The latter remains excited until at some subsequent time the pressure rises to the preselected upper limit, at which time as above described the contacts 26A, 26C again close to energize relay 27 where-upon contact 32C reestablishes the relay hold-in circuit and contact 310 reverses its position to turn off bulb 28L and to turn on bulb 28H.

In brief, the pressure limit indicator 28, because of the memory afforded by the latch-in relay 27, continuously identifies which limit was last attained by the steam pressure and ignores the variations within a band defined by the preselected upper and lower pressure limits.

With the information afforded by the valve-position indicator 24 and the pressure indicators 23 and 28, the rate of generation of steam and the supply of steam can be controlled by the operator, as will now be explained, to match the actual generation to any required generation within the rating of unit 10 with decreased throlling losses. The same pressure-responsive means 25 may be used both for the switch 26 and the meter 23, or the latter may have its own pressure-responsive actuator.

In general, so long as the indicator 24 shows the steam valve 15 is not in any of its high-loss ranges, the required change in output of generator 11 may be obtained and the steam pressure maintained substantially at the set point preselected to suit the boiler design by correspondingly progressively changing the position of steam valve 15 while also controlling the boiler input valve 18. The meter pointer 23B indicates the steam pressure actually existent and the indicator bulbs 28H, 28L indicate whether the pressure last attained its upper or lower limit. When, however, the operator in operating the controllers to follow a demand for increased or decreased generation observes from indicator 24 that the steam valve has or is about to come into one of the high-loss ranges, he leaves one or the other of the valves temporarily in fixed position depending upon the direction in which generation is to be changed and effects the changes in generation solely by varying in the setting of the other valve.

The control procedure is complicated by the circumstance that changing the setting of either the fuel input valve 18 or the steam valve 15 affects both the boiler steam pressure and the rate of flow of steam to the turbine. When the fuel valve opening is increased, both the steam pressure and the rate of steam flow are increased: conversely, when the fuel valve opening is decreased, both the steam pressure and rate of steam flow are decreased. However, when the steam valve opening is increased, the steam flow is temporarily increased but the steam pressure tends to fall: conversely, when the steam valve opening is decreased, the steam flow is temporarily decreased but the steam pressure tends to rise.

Thus, to obtain and maintain a match between the required generation, as indicated by meter 21, and the actual generation, as indicated by wattmeter 22, and with minimum operation of unit with the system valve in any of its high-loss regions requires a rather complicated mode of operation of the controllers 17 and depending upon whether the demand is for increased or decreased generation, whether the steam pressure was last high or last low and whether the steam valve is in a high-loss or low-loss range.

Assuming that the system demand upon unit 10 is for increased generation, as upwardly from Gl (FIG. 3), that indicator 24 shows the steam valve 15 to be in a low-loss range, and that indicator 28 shows the steam pressure in generation has not been attained, the switch 17D is operated to further close the steam valve while the fuel valve is left fixed. This action continues in response to decreasing demand until:

(a) The steam valve is moved below limit LL of the high-loss region, at which time normal control action is resumed, i.e., the steam valve control switch 17D is operated progressively to decrease the opening of valve 15 while the fuel control switches 20D, 20U are manipulated to maintain the steam pressure substantially constant at the set point; or

(b) A set high steam pressure P is reached, at which point the steam valve is left fixed and switch 20D is actuated to further close the fuel valve until steam pressure is reduced to the set point, after which the steam valve alone is further closed until it is moved below limit LL, with ensuring resumption of normal control.

The foregoing as summarized in Table A below may be used as a guide for the operator in performance of a control method which provides for varying generation of unit 10 with minimized throttling losses in generation ranges otherwise corresponding with the high-loss regions H2, H3 etc. (FIG. 2) of the steam valve.

Table A Demand Position Valve 15 Control Action Increased Generation Decreased Generation Low-Loss Range- Increase steam and fuel valve settings Entering or within High-Loss Range.

Low-Loss Range Entering or within High-Loss Range.

last reached its low limit, a proper control procedure for the operator is to actuate the switches 20U and 17U alternately or concurrently until the indicator 24 shows the steam valve 15 has reached the lower limit LL of the next higher high-loss range (HLR of FIG. 3). If by that time the generation demand has not been attained and the indicator 23 then shows that the steam pressure last reached its low limit, the steam valve 15 is left in position LL and further increase in generation is effected solely by actuating switch 20U for further opening of the fuel valve until the generation is increased, as to G2, due to increased steam flow effected by increased steam pressure. Further increase of generation, as to G2, is obtained by additional opening of the fuel valve alone until a set high steam pressure P is reached (bottom curve of FIG. 3). At this point, the fuel valve is kept fixed and the steam valve opening is increased by actuation of switch 17U. Since increased steam flow cannot be maintained without increased steam production, steam pressure will then decrease requiring further and continued opening of the steam valve. When normal pressure P and the upper limit HL are reached, the fuel and steam valves are again operated jointly to meet increasing generation demand at substantially constant pressure, at G3.

Assuming now that the system demand is for decreased generation, as downwardly from G3 (upper curve, FIG. 3), the steam valve control switch 17 and the fuel control switch 20 are manipulated to decrease the generation and to maintain the steam pressure at the set point (lower curve, FIG. 3). This normal parallel-control action is continued until the steam-valve position, as shown by indicator 24, reaches the upper limit HL of a highloss range HLR. If at that time the desired reduction The system shown in FIG. 4 is generally similar to that of FIG. 1 but automatically controls the setting of the fuel and steam valves associated with unit 10 to match the actual generation with the required generation and with minimized throttling losses due to prolonged operation with the steam valve 15 in any of its high-loss ranges. In general, the corresponding elements of both systems are identified by similar reference characters.

In FIG. 4 the information relating to required and actual generation, steam pressure and valve position is converted into electrical signals and applied to a logic circuit which, as hereinafter explained, controls the pairs of gates U17, D17 and U21 D20 respectively associated with the valve motors 16 and 19, the pairs of gates serving as the pairs of switches 17U, 17D and 20U, 20D of FIG. 1.

Specifically in FIG. 4, the high-loss segments T1-T4 of the valve-position indicator 24A control a switch 35 in the input circuit 36 of the Inverter 37, in input circuit 38 of AND-GATE 39 and in input circuit 40 of AND- GATE 41. Specifically, when the valve 15 is in any of its low-loss regions, the switch 35 is closed to apply a signal V to each of such three input circuits. When the valve 15 is in any of its high-loss ranges (HI-H4 of FIG. 3), the switch 35 is open and the Inverter 37 consequentially produces an output signal V which is applied to input line 68 of AND-GATE 53 and to input line 70 of AND-GATE 71.

As in FIG. 1, the Bourdon tube 25, or equivalent, is responsive to the steam pressure supplied from the boiler 14 and is associated with a switch 26 which in turn controls pressure indicator 28 having a memory which stores information concerning the pressure limit last attained. Specifically, the indicator 28 includes two flip-flop circuits L28 and H28 each having two input circuits and an output circuit. When the pressure reaches its upper limit, the closure of contacts 26A, 26C eifects application of a signal to the first or Memory stage of flip-flop H28 and to the second or Erase stage of flip-flop L28. In consequence, the flip-flop H28 produces an output signal P (pressure-high-memorized) which is applied to the input line 42 of AND-GATE 43 and to the input line 44 of AND-GATE 45: the flip-flop L28 is turned off so far as production of any output signal by it is concerned.

When the steam pressure next reaches its lower limit, the closure of contacts 26B, 26C effects application of a low-pressure signal to the first or Memory stage of flip-flop L28 and to the second or Erase stage of flip-flop H28. In consequence, the flip-flop H28 is turned off for discontinuance of signal P and the flip-flop L28 is turned on to produce its output signal P (pressurelow-memorized) for application to the input line 46 of AND-GATE U20, the input line 48 of AND-GATE 49 and input line 50 of AND-GATE 51.

' It is also to be noted that so long as the steam pressure remains at or above its upper limit, a signal P is applied to the input line 52 of AND-GATE 53. This signal, unlike signal P is terminated as soon as contacts 26A, 26C of the pressure-responsive switch 26 separate in re sponse to a fall of steam pressure.

The controller 17A, which may be of the type shown in US. Letters Patent 3,008,072, compares a signal P representative of the actual steam pressure with a signal P representative of the selected set-point pressure. The selected set-point pressure may coincide with P or P in the following description, P has been selected to correspond with P When the steam pressure rises above the set point, the controller 17A produces a pressuredecrease signal P applied to the input line 54 of AND- GATE 39 and to input line 56 of AND-GATE 53. When the steam pressure falls below the set point, the controller 17A produces a pressure-increase signal P applied to the input line 58 of AND-GATE 49.

The controller 20A, which may also be of the type shown in aforesaid Letters Patent, compares a signal G representative of the actual output of generator 11 With a signal G representative of the required output of generator 11. Whenever the required generation exceeds actual generation, the controller 20A produces a generation-increase signal G applied to the input line 60 of AND-GATE U20 and to the input line 62 of AND-GATE 43. When the required generation is less than actual generation, the controller 20A produces a generationdecrease signal G applied to the input line 64 of AND- GATE 51 and to the input line 66 of AND-GATE 45.

The motor 16 is energized in sense to increase the opening of steam valve 15 by the output signal V of OR-GATE U17 which has two input lines 72, 73 respectively forming the output lines of AND-GATES 39 and 43. Thus, the steam valve setting is increased when GATE 39 is opened by the concurrent existence of signals V and P on its input lines 38, 54 and is also increased when GATE 43 is opened by the concurrent existence of signals P and G on its input lines 42 and 62.

The motor 16 is energized in sense to decrease the opening of steam valve 15 by the output signal V of the OR-GATE D17 which has two input lines 74, 75 respectively forming the output lines of AND-GATES 40 and 71. Thus, the steam valve setting is decreased when GATE 49 is opened by the concurrent existence of signals P and P on its input lines 58, 48 and is also decreased when GATE '71 is opened by concurrent existence of signal V on its input line 70 and of signal (P +G as appearing on its input line 76 from the AND-GATE 51 where is symbolic of the AND logic function.

The motor 19 is excited in sense to increase the opening of the fuel valve 18 and so increase the heat and/ or other input of boiler 14 by the output signal H of 8 AND-GATE U20. Thus, the fuel valve setting is increased when GATE U20 is opened by concurrent existence of signals P and G on its input lines 46 and 60.

The motor 19 is energized in sense to decrease the setting of fuel valve 18 by the output signal H of the OR-GATE D20 which has three input lines 77, '78, 79. The first input line 77 is from AND-GATE 53 so that OR-GATE D20 is open when the signals P P and V concurrently exist on the three input lines 56, 52, 68 of AND-GATE 53. The second input line 78 of OR-GATE D20 is from the AND-GATE 41 so that GATE D20 is opened by concurrent existence of signals V and (P |G on the input lines 40 and of GATE 41. Thethird input line 79 of OR-GATE D20 is from the AND-GATE 45 so that GATE D20 is open for concurrent existence of signals G and P on the input lines 66 and 44 of AND-GATE 45.

(A) From the foregoing it thus appears that when thereis a requirement for increased generation while the valve 15 is in a low-loss region and with the steam pressure most recently at its lower limit, the signal G; from the controller 20A and the signal P from pressure Memory L28 are jointly effective to produce a signal H calling for increased rate of production of steam by the boiler, i.e.:

( GI+P LM:H I

where indicates the control action. Also for the above stated operating conditions, the setting of steam valve 15 is either increased or decreased depending upon the existing steam pressure. If the pressure is above the set point, the signal PD of controller 17A and the V signal are jointly effective to produce a signal V for increased opening of steam valve 15, i.e.:

( D i' R I If, on the other hand, the steam pressure is at or below the set point, the signal P; of controller 17A and the signal P are jointly effective to produce a signal V for decreased opening of steam valve 15, i.e.:

(B) Again assuming the requirement for increased generation with the steam pressure most recently at its lower limit but with the valve 15 approaching or in a high-loss region, the generation-increase signal G of controller 20A and the signal P are jointly effective to produce signal H; for increased opening of fuel valve 18 (see Eq. 1) until the steam pressure rises to its upper limit. If or when the steam pressure rises to the upper limit, the signals V and P can combine with a pressure-decrease signal P from the controller 17A to produce a signal H for reducing the setting of fuel valve 18, i.e.:

Also for the initial set of assumed conditions under B the steam pressure can be increased, but not decreased, by a control action involving controller 17A and steam valve 15. Specifically, the pressure signal P can combine with a concurrent pressure-increase signal P; to produce a signal V for reducing the setting of steam valve 15 (Eq. 3). However, because of absence of the low-loss range signal V a pressure decrease signal P from controller 17A is ineffective to produce a signal V for increasing the setting of valve 15.

(C) Now again assuming a requirement for increased generation with steam valve 15 approaching or in a highloss region but with the steam pressure most recently at its upper limit, the G signal of controller 20A and the signal P are jointly effective to produce a signal V for increased opening of steam valve 15 until the steam pressure falls to its lower limit, i.e.:

(5) ri- HM VI For this third set of assumed operating conditions, the controller 17A cannot cause action of steam valve 15 in 9 either direction because in absence of signal V the existence of a pressure-decrease signal P cannot produce a signal V for opening of valve 15 and because in absence of signal P the existence of a pressure-increase signal P; cannot produce a signal V for closing of steam valve 15. It with valve 15 initially in a low-loss region there is a demand for increased generation which is satisfied before valve 15 is moved up to the next higher highvloss region, the automatic control action is that of paragraph A above: if there is a further demand for increased generation causing the valve 15 to be moved up to the high-loss region, the resulting automatic control action is that of paragraph B or C, or both in alternation. This commonly results in movement of valve 15 to the lower end of the next low-loss region so that for any further required increase in generation the resulting automatic control action again proceeds in accordance with paragraph A to obtain a match between the actual and required generation.

(D) Now assuming there is a requirement for decreased generation with steam valve 15 in a low-loss region and with the steam pressure most recently at its lower limit, the G signal of controller 20A, the P signal and the V signal (see GATES 51 and 41) are jointly effective to produce signal H for decreased setting of the fuel valve 18, i.e.:

If the steam pressure falls below its lower limit, a P signal from controller 17A combines with a P signal to produce a signal V for decreased setting of the steam valve (see Eq. 3); if steam pressure rises above the low limit, a P signal from controller 17A combines with the V signal to produce a signal V for increased setting of the steam valve 15 (see Eq. 2).

(E) Again assuming there is a requirement for decreased generation with the steam pressure most recently at its lower limit but with the steam valve 15 approaching or in a high-loss region, the G signal from controller 20A, the P signal and the V signal are jointly effective to produce V signal for reducing the setting or opening of steam valve 15, i.e.:

For these assumed conditions, controller 17A is ineffective to open the steam valve. If it is producing a pressure-increase signal P that signal jointly with the P signal is effective to produce a V signal, decreasing the opening of valve 15 (see Eq. 3). If the steam pressure rises to its upper limit, the P signal of switch 26 and the V signal combines with the P signal of controller 17A to produce an H signal for reducing the opening of fuel valve 18 (see Eq. 4). Otherwise, the previous control action (Eq. 7) proceeds until valve 15 is moved beyond the lower limit of the high-loss region and further decrease in generation is effected by the control action of paragraph D.

(F) Again assuming there is a requirement for decreased generation with the steam valve 15 approaching or in a high-loss region but with the steam pressure most recently at its upper limit, the generation-decrease signal G of controller 20A combines with the F signal to produce an H signal for reducing the opening of fuel valve 18, i.e.:

This action may continue until the pressure is reduced to its lower limit whereupon any further required reduction of actual generation is obtained in accordance with the control action of paragraph E. If still further reduction in actual generation is required, the control action then becomes that of paragraph D.

In brief summary, the steam valve is opened to increase the actual generation G if the steam pressure has recently been at its upper limit (Eq. and is opened to decrease the steam pressure if such valve is in a low-loss range (Eq. 2). The steam valve 15 is closed to decrease the actual generation G if the steam pressure has recently been at its lower limit and valve 15 is approaching or in a high-loss range (Eq. 7); and is closed to increase the steam pressure if the pressure was most recently at its lower limit (Eq. 3). The fuel valve 18 is opened to increase the actual generation G if the steam pressure has most recently been at its lower limit (Eq. 1). The fuel valve 18 is closed to decrease generation either if the steam pressure was most recently at its upper limit (Eq. 8) or if the steam pressure was most recently at its lower limit and the steam valve is in a low-loss range (Eq. 6); and is closed to decrease the steam pressure if the steam valve 15 is approaching or in a high-loss range and the steam pressure is at its upper limit (Eq. 4).

It is to be understood that all of the foregoing control actions, automatically effected by the system of FIG. 4 in response to recognition by the logic circuitry of the specified operating variables, may be effected manually with the system of FIG. 1. With the latter, performance of the method of course requires the operator properly to interpret the information provided by the various indicators and then to make the proper decisions in selective operation of the control switches 17U and 17D, 20U and 20D.

It is also to be understood that the execute signals from the GATES U17, D17, U20 and 20D of FIG. 4 may be used in a semi-automatic system to indicate to an operator when the steam valve is to be opened or closed and when the heat-input to the boiler is to be increased or decreased. In such semi-automatic system, the decision concerning a proper control of the steam valve and of steam production for the then existent operating conditions is made by the logic circuitry of FIG. 4 instead of by the operator who need only execute the command without need to collate the signal information.

It is also to be understood that full-automatic or semiautomatic execution of the method of load-matching with minimum throttling losses is not limited to use of the particular logic circuits and elements specifically shown but comprehends equivalents within the scope of the appended claims.

What is claimed is:

1. A method of minimizing steam losses in control of a generating unit including a generator, a prime-mover and a boiler and having steam valve means with high and low-loss ranges alternating in the full travel range of said valve means which comprises in response to a demand for increased generation,

varying the rate of steam production and the valve opening to maintain the steam pressure substantially constant until the lower limit of of the next higher high-loss range is reached, then with said valve means left stationary increasing the rate of steam production so long as the steam pressure does not exceed a preselected upper limit, then with constant rate of steam production opening said valve means to the upper limit of said higher high-loss range and, then varying the rate of steam production and the valve opening to maintain the steam pressure constant for further change in generation,

and, in response to a demand for decreased generation varying the rate of steam production and the Valve opening to maintain the steam pressure substantially constant until the upper limit of the next lower high-loss range is reached, then with the constant rate of steam production closing the valve means until it reaches the lower limit of said high-loss range provided that the steam pressure does not exceed a preselected upper limit, then varying the rate of steam production concurrently with closing of the valve means to maintain the steam pressure constant for further change in generation.

2. A method of minimizing steam losses in control of a generating unit including a generator, a primemover and a boiler and having steam valve means with high and low-loss ranges alternating in the full travel range of said valve means which comprises Increasing the steam valve opening when (a) there exists a demand for increased generation and provided that the steam pressure last attained a preselected upper limit,

(b) the steam pressure is above a preselected set point and provided that the valve means is in a low-loss range,

decreasing the steam valve opening when (c) there exists a demand for decreased generation and provided that the steam pressure last attained a preselected lower limit and that the valve means is approaching or in a high-loss range,

(d') the steam pressure is low,

increasing the rate of production of steam when (e) there exists a demand for increased generation and provided the steam pressure last attained said lower limit, and

decreasing the rate of production of steam when (t) there exists a demand for decreased generation and provided that the valve means is in a low-loss range and the steam pressure last attained said lower limit,

(g) there exists a demand for decreased generation and provided that the steam pressure last attained said upper limit,

(h) the steam pressure is at said upper limit and provided that the valve means is in a high-loss range.

3. A method of minimizing steam losses in control of a generating unit including a generator, a prime-mover anda boiler and having steam valve means with high and low-loss ranges alternating in the full travel range of said valve means which comprises increasing the generation by (a) increasing the steam valve opening provided that Tthe steam pressure last attained a preselected upper limit,

(b) increasing the rate of steam production provided that thesteam pressure last attained a preselected lower limit,

decreasing the generation by (c) decreasing the steam valve opening provided that the steam pressure last attained a preselected lower limit and the valve means is approaching or in a high-loss range,

((1) decreasing the rate of steam production provided that the steam pressure last attained said lower limit and the valve means is in low-loss range,

(e) decreasing the rate of steam production provided that the steam presurelast attained its said upper limit,

increasing the steam presure by (f) decreasing the steam valve opening provided the steam pressure last attained its said lower limit,

and decreasing the steam pressure by (g) increasing the steam valve opening provided that the steam valve is in a low-loss range,

(h) decreasing the rate of steam production provided that the valve means is approaching or in a high-loss range and the steam pressure attains its said upper limit.

4. A control system for a generating unit including a generator, a boiler having input means adjustable to vary its rate of production of steam, and a prime-mover having an input valve means with high and low-loss ranges in its full travel range, said control system comprising position-responsive means for indicating whether said valve is in a high-loss range or a low-loss range,

pressure-responsive means for indicating the relation between the existing steam presure and a preselected set point,

memory means for indicating whether the steam pressure last attained a preselected lower limit or a preselected upper limit, and generation-responsive means for indicating the relation between existing generation and required generation,

said position-responsive means, said pressure-responsive means, said memory means and said generationresponsive means jointly providing information necessary for adjustment of both of said input means in achieving desired generation of said unit with minimized operation of said unit with said valve means in a high-loss range. 5. A control system for a generating unit including a generator, a boiler having input means adjustable to vary its rate of production of steam, and a prime-mover having an input valve means with high and low-loss ranges in its full travel range, said control system comprising position-responsive means for indicating to an operator whether said valve is in a high-loss range or a lowloss range, pressure-responsive means for indicating to the operator the relation between the existing steam presure and a preselected set point, memory means for indicating to the operator whether the steam pressure last attained a preselected lower limit or a preselected upper limit, and

generation-responsive means for indicating to the operator the relation between the existing generation and the required generation, said position-responsive means, said pressure-responsive means, said memory means and said generationresponsive means jointly providing the operator with information necessary for adjustment of both of said input means in achieving desired generation with minimized operation of said unit with said input valve means in a high-loss range. 6. A control system for a generating unit including a generator, a boiler having input means adjustable to vary its rate of production of steam, and a prime-mover having input valve means with high and low-loss ranges in its full travel range, said control system comprising position-responsive means for producing electrical signals respectively indicative of high and low-loss range positions of said valve means,

pressure-responsive means for producing electrical signals respectively indicative of steam-pressure deviations above and below a set point and attainment of a preselected upper limit, memory means for producing electrical signals respectively indicative of whether the steam pressure last attained its upper limit or a preselected lower limit,

generation-responsive means for producing electrical signals respectively indicative of a demand for increased generation and a demand for decreased generation, and

a logic circuit to which said signals are applied as inputs to produce output signals controlling the adjustment of both of said input means for achieving desired generation of said unit with minimum operation of said unit with said input valve means in a high-loss range.

7. A control system for a generating unit including a generator, a boiler having input means adjustable to vary its rate of production of steam, and a prime-mover having input valve means with high and low-loss ranges in its full travel range, said control system comprising position-responsive means for producing electrical signals (V V respectively indicative of low-loss and high-loss range positions of said valve means,

pressure-responsive means for producing electrical signals (P P P respectively indicative of steampressure deviations above and below a set point and attainment of a preselected upper pressure limit,

memory means for producing electrical signals (P P respectively indicative of Whether the steam pressure last attained its upper limit or a preselected lower limit,

generation-responsive means for producing electrical signals (G G respectively indicative of a demand for increased generation and a demand for decreased generation, and a logic circuit to which said signals are applied as inputs to product output signals (V V H H said output signal V being produced for opening of said input valve means upon coexistence of input signals P and V and upon coexistence of input signals G and P said output signal V being produced for closing of said input valve means upon coexistence of input signals P and P and upon coexistence of input signals G P and V said output signal H being produced for adjustment of said boiler input means in sense to increase the production of steam upon coexistence of signals G and PLM,

and said output signal H being produced for adjustment of said boiler input means in sense to decrease the production of steam upon coexistence of signals P P and V upon coexistence of signals G P and V and upon coexistence of signals G and PHNI.

8. A control system for a generating unit including a generator, a boiler having motor-operated means adjustable to vary its heat input, and a prime-mover having motor-operated steam valve means with high and lowloss throttling ranges in its full travel range, said control system comprising position-responsive means for producing high-loss and low-loss signals respectively indicative of positions of said valve means in said high-loss and low-loss ranges,

pressure-responsive means for producing signals indicative of deviations of steam pressure from a set point, memory means for producing signals indicative of whether the steam pressure last attained a preselected upper limit or a preselected lower limit, generation-responsive means for producing signals indicative of demands for increased and decreased generation, and

control means responsive to said signals to effect operation of the steam valve motor in valve-opening direction upon coexistence of signals indicative of a low-loss valve position and a pressure-deviation above set point; and upon coexistence of signals indicative of a demand for increased generation and of last attainment by system pressure of said upper limit;

to efiect operation of said steam-valve motor in valve-closing direction upon coexistence of signals indicative of a demand for decreased generation, of high-loss valve position and of last attainment by steam pressure of said lower limit; and upon existence of low stream pressure;

to effect operation of the boiler-input motor in input-increasing direction upon coexistence of signals indicative of a demand for increased generation and of last attainment by steam pressure of said lower limit; and to effect operation of the boiler-input motor in input-decreasing direction upon coexistence of signals indicative of a high-loss valve position and of attainment by steam-pressure of said upper limit; upon coexistence of signals indicative of a low-loss valve position, a demand for decreased generation and of last attainment by steam pressure of said lower limit; and upon coexistence of signals indicative of a demand for decreased generation and of attainment by steam-pressure of said upper limit. 9. A control system for a generating unit including a generator, a boiler having input means adjustable to vary its rate of production of steam, a prime-mover having an input valve means with high and low-loss ranges in its full travel range, said control system comprising position-responsive means for indicating whether said valve is in a high-loss range or a low-loss range,

pressure-responsive means for indicating the relation between the existing steam pressure and a preselected set point,

memory means for indicating whether the steam pressure last attained a preselected lower limit or a preselected upper limit, and generation-requirement means for indicating a required change of generation, said position-responsive means, said pressure-responsive means, said memory means and said generation-requirement means jointly providing information necessary for adjustment of both of said input means in achieving desired generation of said unit with minimized operation of said unit with said valve means in a high-loss range. 10. A control system for a generating unit including a generator, a boiler having input means adjustable to vary its rate of production of steam, and a prime-mover having an input valve means with high and low-loss ranges in its full travel range, said control system comprising position-responsive means for indicating to an operator whether said valve is in a high-loss range or a lowloss range, pressure responsive means for indicating to the operator the relation between the existing steam pressure and a preselected set point,

memory means for indicating to the operator whether the steam pressure last attained a preselected lower limit or a preselected upper limit, and

generation-requirement means for indicating to the operator a required change of generation,

said position-responsive means, said pressure-responsive means, said memory means and said generationrequirement means jointly providing the operator with information necessary for adjustment of both of said input means in achieving desired generation with minimized operation of said unit with said input valve means in a high-loss range.

References Cited by the Examiner UNITED STATES PATENTS ORIS L. RADER, Primary Examiner. 

1. A METHOD OF MINIMIZING STEAM LOSSES IN CONTROL OF A GENERATING UNIT INCLUDING A GENERATOR, A PRIME-MOVER AND A BOILER AND HAVING STEAM VALVE MEANS WITH HIGH AND LOW-LOSS RANGES ALTERNATING IN THE FULL TRAVEL RANGE OF SAID VALVE MEANS WHICH COMPRISES IN RESPONSE TO A DEMAND FOR INCREASED GENERATION, VARYING THE RATE OF STEAM PRODUCTION AND THE VALVE OPENING TO MAINTAIN THE STEAM PRESSURE SUBSTANTIALLY CONSTANT UNTIL THE LOWER LIMIT OF OF THE NEXT HIGHER HIGH-LOSS RANGE IS REACHED, THAN WITH SAID VALVE MEANS LEFT STATIONARY INCREASING THE RATE OF STEAM PRODUCTION SO LONG AS THE STEAM PRESSURE DOES NOT EXCEED A PRESELECTED UPPER LIMIT, THEN WITH CONSTANT RATE OF STEAM PRODUCTION OPENING WITH VALVE MEANS TO THE UPPER LIMIT OF SAID HIGHER HIGH-LOSS RANGE AND, THEN VARYING THE RATE OF STEAM PRODUCTION AND THE VALVE OPENING TO MAINTAIN THE STEAM PRESSURE CONSTANT FOR FURTHER CHANGE IN GENERATION, AND, IN RESPONSE TO A DEMAND FOR DECREASED GENERATION VARYING THE RATE OF STEAM PRODUCTION AND THE VALVE OPENING TO MAINTAIN THE STEAM PRESSURE SUBSTANTIALLY CONSTANT UNTIL THE UPPER LIMIT OF THE NEXT LOWER HIGH-LOSS RANGE IS REACHED, THEN WITH THE CONSTANT RATE OF STEAM PRODUCTION CLOSING THE VALVE MEANS UNTIL IT REACHES THE LOWER LIMIT OF SAID HIGH-LOSS RANGE PROVIDED THAT THE STEAM PRESSURE DOES NOT EXCEED A PRESELECTED UPPER LIMIT, THEN VARYING THE RATE OF STEAM PRODUCTION CONCURRENTLY WITH CLOSING OF THE VALVE MEANS TO MAINTAIN THE STEAM PRESSURE CONSTANT FOR FURTHER CHANGE IN GENERATION.
 5. A CONTROL SYSTEM FOR A GENERATING UNIT INCLUDING A GENERATOR, A BOILER HAVING INPUT MEANS ADJUSTABLE TO VARY ITS RATE OF PRODUCTION OF STEAM, AND A PRIME-MOVER HAVING AN INPUT VALVE MEANS WITH HIGH AND LOW-LOSS RANGES IN ITS FULL TRAVEL RANGE, SAID CONTROL SYSTEM COMPRISING POSITION-RESPONSIVE MEANS FOR INDICATING TO AN OPERATOR WHETHER SAID VALVE IS IN A HIGH-LOSS RANGE OR A LOWLOSS RANGE, PRESSURE-RESPONSIVE MEANS FOR INDICATING TO THE OPERATOR THE RELATION BETWEEN THE EXISTING STEAM PRESSURE AND A PRESELECTED SET POINT, MEMORY MEANS FOR INDICATING TO THE OPERATOR WHETHER THE STEAM PRESSURE LAST ATTAINED A PRESELECTED LOWER LIMIT OR A PRESELECTED UPPER LIMIT, AND GENERATOR-RESPONSIVE MEANS FOR INDICATING TO THE OPERATOR THE RELATION BETWEEN THE EXISTING GENERATION AND THE REQUIRED GENERATION, SAID POSITION-RESPONSIVE MEANS, SAID PRESSURE-RESPONSIVE MEANS, SAID MEMORY MEANS AND SAID GENERATIONRESPONSIVE MEANS JOINTLY PROVIDING THE OPERATOR WITH INFORMATION NECESSARY FOR ADJUSTMENT OF BOTH OF SAID INPUT MEANS IN ACHIEVING DESIRED GENERATION WITH MINIMIZED OPERATION OF SAID UNIT WITH SAID INPUT VALVE MEANS IN A HIGH-LOSS RANGE. 